169 The Journal of Experimental Biology 212, 169-177 Published by The Company of Biologists 2009 doi:10.1242/jeb.024505 Temperature adaptation of cytosolic malate dehydrogenases of limpets (genus Lottia): differences in stability and function due to minor changes in sequence correlate with biogeographic and vertical distributions Yunwei Dong* and George N. Somero† Hopkins Marine Station, Department of Biology, Stanford University, Pacific Grove, CA 93950, USA *Current address: The Key Laboratory of Mariculture, Ministry of Education, Fisheries College, Ocean University of China, Qingdao, Peopleʼs Republic of China 266003 †Author for correspondence (e-mail:
[email protected]) Accepted 28 October 2008 SUMMARY We characterized functional and structural properties of cytoplasmic malate dehydrogenases (cMDHs) from six limpets of the genus Lottia that have different vertical and latitudinal distributions. Particular attention was given to the cryptic species pair Lottia digitalis (northern occurring) and L. austrodigitalis (southern occurring) because of recent contraction in the southern range of L. digitalis and a northward range extension of L. austrodigitalis. As an index of adaptation of function, we measured the NADH NADH effects of temperature on the apparent Michaelis–Menten constant (Km) of the cofactor NADH (Km ). Km values of cMDHs from the mid- to high-intertidal, low-latitude species L. scabra and L. gigantea were less sensitive to high temperature than those of cMDHs from the low- and mid-intertidal, high-latitude species L. scutum and L. pelta. cMDH of L. digitalis was more sensitive to high temperatures than the cMDH ortholog of L. austrodigitalis. Thermal stability (rate of loss of activity at 42.5°C) showed a similar pattern of interspecific variation.